Complexes lanthanide ions

When not complexed, lanthanide ions have a high affinity for bone in vivo because they act as calcium ion mimics. Because the lanthanides undergo hydrolysis above a pH of 4, they readily form radiocolloids when not complexed, and are then taken up by the liver. This bone and liver uptake results in non-specific radiation doses to non-target (normal) tissues and organs and is undesirable.91 The polyaminocarboxylate class of ligands are considered to be the optimal choice for the basis of BFCAs for the+3 metal cations, including the lanthanides. It is essential that the... 

The ligand absorbs light efficiently and transfers the energy to the complexed lanthanide ion. 

Lanthanide ions have a high affinity for hard donor atoms, and ligands containing oxygen or oxygen-nitrogen atoms may be employed in the preparation of lanthanide polymeric complexes. Lanthanide ions present only little preference in bond direction, due to the inner positioning of their 4f valence orbitals. 

The intensities of the induced electric dipole transitions in lanthanide ions are not much affected by the environment. The dipole strength of a particular transition of a lanthanide ion in different matrices will not vary more than a factor two or three. However, a few transitions are very sensitive to the environment, and these are usually more intense for a complexed lanthanide ion than for the lanthanide ion in aqueous solution. The intensity increases up to a factor 200 (Gruen and DeKock 1966, Gruen et al. 1967). Only in a few cases has a lower intensity than in the aqueous solution been reported for these transitions (e.g. Krupke 1966). Jorgensen and Judd (1964) have called such transitions hypersensitive transitions. They noted that all known hypersensitive transitions obey the selection rules A5 = 0, AI 2 and jAJj 2. These selection rules are the same as the selection rules of a pure quadrupole transition, but calculations have revealed that the intensities of hypersensitive transitions are several orders of magnitude too large for these transitions to have a quadrupole character. Therefore, hypersensitive transitions have been called also pseudo-quadrupole transitions. No quadrupole transitions have been observed for lanthanide ions, although Chrysochoos and Evers (1973) stated that the intensity of the hypersensitive transitions D2 Fq (in the absorption spectrum) and Do Fi (in the luminescence spectrum) of Eu " are mainly quadrupolar in nature. 

The reason why lanthanides of high atomic number emerge first is that the stability of a lanthanide ion-citrate ion complex increases with the atomic number. Since these complexes are formed by ions, this must mean that the ion-ligand attraction also increases with atomic number, i.e. that the ionic radius decreases (inverse square law). It is a characteristic of the lanthanides that the ionic radius... 

Fig. 11) form very strong and selective complexes with Fe or actinide and lanthanide ions (63,64) while a similar receptor with hard endocarboxyhc acid groups is efficient for hard and ions showing again responsibility of a charge density effect in the receptor—substrate recognition (65). Thus,... 

Complexes of lanthanide ions with N-donor ligands. J. H. Forsberg, Coord. Chem. Rev., 1973,10, 195-226 (129). 

The second class of reaction is that of processes in which the 4f electrons are conserved. The obvious examples are the complexing reactions of tripositive lanthanide ions. Here the irregularities due to changes in inter-electronic repulsion almost entirely disappear. We then get the slight smooth energy change whose consequences were so familiar to 19 century chemists, who struggled vdth the separation problem. 

Fig. 1.2 Standard enthalpy changes of (a) the complexing of lanthanide ions in aqueous solution by EDTA" ( left-hand axis) (b) the standard enthalpy change of reaction 2, the dichloride being a di-f...

Assays based on luminescent lanthanide ions were developed initially in the 1970s, when instrumentation became available which could distinguish long-lived luminescence from a shortlived background. Leif and co-workers reported the first attempts to use lanthanide complexes (in this case europium complexes with 1,10-phenanthroline and 7-diketonates, i.e., [Eu(phen)(diketo-nate)3]) as tags for antibodies.107 These proved kinetically unstable in the pH regime required... 

Lanthanide ions have been used as DEFRET acceptors in split probes for DNA sequence such as shown in Figure 15.137 When using europium and terbium complexes, the choice of chromo-phores is rather restricted, owing to the high-energy emissive states associated with these ions (vide supra). In this case, the donor chromophore is a salicylic acid unit appended to an... 

It is evident that the approach described so far to derive the electronic structure of lanthanide ions, based on perturbation theory, requires a large number of parameters to be determined. While state-of-the-art ab initio calculation procedures, based on complete active space self consistent field (CASSCF) approach, are reaching an extremely high degree of accuracy [34-37], the CF approach remains widely used, especially in spectroscopic studies. However, for low point symmetry, such as those commonly observed in molecular complexes, the number of CF... 

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